import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

// 封装了针对用户表的相关操作
public class UserDao {
    // 根据用户名来查询用户的详情 -- 登陆
    // 隐含约束: 用户名需要唯一.
    public User selectByName(String username) {
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        try {
            // 1. 和数据库建立连接
            connection = DBUtil.getConnection();
            // 2. 构造 SQL
            String sql = "select * from user where username = ?";
            statement = connection.prepareStatement(sql);
            statement.setString(1, username);
            // 3. 执行 SQL
            resultSet = statement.executeQuery();
            // 4. 遍历结果集合
            if (resultSet.next()) {
                User user = new User();
                user.setUserId(resultSet.getInt("userId"));
                user.setUsername(resultSet.getString("username"));
                user.setPassword(resultSet.getString("password"));

                return user;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(connection, statement, resultSet);
        }
        return null;
    }

    // 根据用户 id 来查询用户详情 -- 在获取用户信息的时候, 需要用到.
    public User selectById(int userId) {
        Connection connection = null;
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        try {
            // 1. 和数据库建立连接
            connection = DBUtil.getConnection();
            // 2. 构造 SQL
            String sql = "select * from user where userId = ?";
            statement = connection.prepareStatement(sql);
            statement.setInt(1, userId);
            // 3. 执行 SQL
            resultSet = statement.executeQuery();
            // 4. 遍历结果集合
            if (resultSet.next()) {
                User user = new User();
                user.setUserId(resultSet.getInt("userId"));
                user.setUsername(resultSet.getString("username"));
                user.setPassword(resultSet.getString("password"));
                return user;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(connection, statement, resultSet);
        }

        return null;
    }
}
